


Hidden Within My Heart

by Nighthowler252



Category: Undertale (Video Game)
Genre: Alternate Universe - Soulmates, F/M, M/M, Other Additional Tags to Be Added, Reader has nicknames, reader goes by moon
Language: English
Status: In-Progress
Published: 2020-04-23
Updated: 2020-04-27
Packaged: 2021-03-02 01:40:31
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 1,768
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23797057
Author URL: https://archiveofourown.org/users/Nighthowler252/pseuds/Nighthowler252
Summary: Cross is close with a girl that goes by Moon, Cross (and Chara) is slowly but surely starting to fall for her. When they learn that she had been hiding something from them, how will they react?
Relationships: Cross!Chara/Reader, Cross!Sans/Reader, Ink/Error, Nightmare & Cross, Sans/Reader
Kudos: 37





	1. Prologue

**Summary for the Chapter:**

> Cross meets up with a friend

Cross had always liked this AU where Monsters and Humans were friends, but the best part about it was that there was no Sans or Papyrus! Cross had been coming to this AU for a while although he never told Nightmare or the rest of the Gang. The main reason he preferred to come to this AU was because of one reason... he found  _ her _ .

"Cross?" A female voice said from behind him, making the skeleton spin around and hug the human.

"Hey there moonlight!" He said, making the human blush a little. Cross acquired the nickname for this girl when they first met, she was on a hill where he was portal hopping for codes. She was just a silhouette in the moonlight, when she turned he could swear that he was staring at an angel from the heavens. Cross never really liked to hug or talk to people other than his family or that are a part of the gang but when he met this girl something felt right. So he stuck around, he’d visit every Friday when Nightmare had to do paper work and everyone else was doing their own things but for a change he didn’t come to see her on a Friday.

"What are you doing here?" She asked. It was true, Cross just shrugged his shoulders and hugged her shoulders a little tighter only for her to return the embrace. Cross mentally laughed, he really had trusted this girl after only knowing her for six months. He’d told her about Chara, the X Event, being a part of Nightmare’s gang, he even told her that his world was forever gone, he’d told her everything and she just listened, not judging him.

“I just wanted to surprise you is all, ever since the… X Event happened I’ve been a little– how to put this… clingy?” Cross answered, he never really bothered to ask anyone for hugs or attention– well other than Nightmare– until he met this girl. Whenever he was near her his shared soul would thump like a drum and he’d feel at ease. So he just melted into the hug letting his soul drum in his chest and feeling her own do the same.

She and Cross continued to hug for a few minutes before she took a step back. Her waist long brown hair seemed to glow in the afternoon light and her amber eyes shined with life. Cross looked to the ground then made a slight grabby motion towards her, she must have noticed because she took his hand in her own. "Has Chara been giving you a hard time?"

"No... he's been okay." Cross muttered, before he knew it he pulled her into a hug. “I just want to be with you today… Moon.”


	2. Plot start

**Summary for the Chapter:**

> Moon tells Cross and Chara that there's more to her world than Monsters and Humans...

**Notes for the Chapter:**

> So! I should explain something, the reason why the reader's name is Moon and this is written in third person view. I was taught to write in either first or third person view and use real names (not saying Y/N isn't a real name) so it's just kinda wired into my brain to do that, but if you want you can use Y/N as a filler I honestly don't mind. Personally my mind fills it in as Yin, so do what you wish.

Cross and Moon wandered around for a while, Cross still wasn’t willing to let Moon go. Chara would tease him whenever Cross would make a grabby hand motion towards Moon. For some reason he just didn’t want to be away from her for very long, it was odd. 

“Hey Cross, Chara, do you wanna go to Muffet’s?” Moon asked. Cross had always found it fascinating that she could see Chara when no one could (well no one other than himself and Dust’s brother) but Moon seemed to be different. It was as though she couldn’t exactly see Chara but instead feel his presents. 

“Sure! I’d like something a little sweet, what about you Chara?” Said ghost just shrugged, they began to walk and joked around. Just before they went into the spider monster’s café Moon stopped, her entire demeanor changed within a second. “Something wrong, Moonlight?”

“Cross we need to talk… it’s nothing bad I promise but I need to tell you something about this world.” Cross was interested in what she wanted to tell him about her AU, he wondered what made it different from all the others. Before he could voice his questions Moon walked into Muffets and sat down in a booth, Cross and Chara followed and sat on the opposite side. Muffet came over and got their orders, Moon got a strawberry banana smoothie with an apple pie and Cross got a chocolate milkshake. Once Muffet left to get their orders, Moon sighed. “In this AU there are Humans, Monsters and a species that people call the Shadows. These are a surface types of Monsters, there’s only three that are known throughout the world. Werewolves, Vampires, and Wendigos.”

Moon paused allowing Cross so absorb the information she just gave him. Cross looked to Chara, who nodded so Cross made a motion for Moon to continue. Before she could though Muffet came back with their food. With a small smile Moon thanked the monster then turned back to Cross and Chara. 

“Now before I continue I need to tell you about their souls. Shadow’s souls are a mix between Monster and Human, they have traits like a Human’s but are upside down like a Monster’s. Though there is one thing that makes them extremely unique… it’s that they have a  _ shadow _ around their souls.” Moon’s voice seemed very far away as though she knew this from experience. “Shadow’s are also able to make their souls look like a human’s, that's how the ones with a human appearance hide in plain sight. Each one has a different name, the Shadow Wolves, Shadow Pires and Shadow Wendigos. Cross the reason why I’m telling you this is because I wanted your opinion on them.”

Cross paused, he had never heard of these things before he’d met a few from other AUs but he’d never heard them called ‘Shadows’ before. He wondered why she was telling him this. “From what I understand, they seem interesting. Chara doesn’t really care but I wouldn’t mind meeting one.”

Moon seemed to relax at his answer, Cross noticed that Chara’s eyes narrowed at their friend. Before Cross or Moon could say anything more her phone began to ring, with an apology she answered it. Cross and Chara said their goodbyes, they left and made their way back to the hideout Cross needed to talk with Error about these ‘Shadows’.

**Notes for the Chapter:**

> Thank you all for putting up with my writing! This story is going to be kinda all over the place but I will say when it's a short filler chapter and when it's plot based (plot will look like ) so if you just want plot then look for those! Thank you again! Have a good life! (P.S. when ever it's Moon's POV it wont be third person view it'll be second person view)


	3. Learning more about The Shadows

**Summary for the Chapter:**

> Getting to learn more about the Shadows and meeting Ink, Error and Nightmare!

Once Cross had entered Nightmare’s castle later that night, he ignored Horror, Dust and Killer when they greeted him. Cross only had one thing on his mind, why was Moon acting like she was hiding something? It was eating away at his soul, he’d only known her for six months. It wasn’t like they were– he froze. Why was he thinking this of all things? It was impossible! Error, Ink, Nightmare and himself all thought that since sharing his soul with Chara, he was unable to have one.

Subconsciously his skeletal hand reached up and under the caller of his shirt, pulling out a medallion. Cross didn’t just wear the golden heart locket but also a medallion that he had gotten from Moon a month after they had met. This medallion was silver about the size of a quarter and had a wolf paw print embedded into it, Moon had a similar one but the print on hers stuck out. She had said that it was something her mom gave her before leaving home, it was a family heirloom. Cross had never understood why she would have given him this, it seemed to be a matching set. One that was meant for…  _ lovers _ .

Cross was now extremely confused and a little worried. Did Moon have feelings for him? Why was she hiding things? Did she not trust him enough to tell him? He had so many questions with very sparse answers. So he made his way to Nightmare’s throne room. If anyone knew about this sort of thing it was Nightmare and Error. Once he made his way to the large double doors, Cross opened them without any warning. Nightmare and Error were in there as he suspected the thing that he wasn’t expecting though was that Ink was there sitting next to Error. 

“ **What’s the meaning of this, Cross?** ” Nightmare’s voice echoed through the dark throne room. Cross bowed slightly before walking all the way into the room, Error moved slightly so he was in front of Ink. It made sense since they were mates and had a soulling on the way.

“I need to speak with you and Error about creatures called ‘The Shadows’ seeing as Error knows about anonimallies and you know about darkness. I figured you’d know something about them.” Was all Cross said before he began to play with his heart locket. He still hadn’t told them about Moon just yet, worried about what they’d do. Error looked to Ink– who was very confused– then to Nightmare, they shared a glance. Which was all they had to do for Cross to figure out that they knew something. “What do you know?”

“ShAdOwS– “Error was cut off by Ink touching him, with a sigh Error started again just less glitchy. “Shadows are creatures that have only three races, Wolves, Pires and Wendigos. Each one has a human form– unless rabid or feral– have a tattoo somewhere on their being to show their clan and rank. For Wolves its a moon tattoo the more filled in it is the lesser the rank. Pires its the most bats is the higher the rank, and for Wendigos the more teeth on a skull tattoo or the more claw marks.”

“ **If someone is a descendant of one of the first shadows they will have an enchanted item to protect the one they have claimed as a potential mate. I’m not exactly sure what the Wolf Clan’s is, but the Pires have matching rings and the Wendigo Clan has matching pendants. Cross if this is about that girl you’ve been hanging around for the last six months then you should say so.** ” Cross tensed up. Was Nightmare planning anything to hurt Moon? “ **Don’t worry I’m fine with you being around her, I’m glad that you have found someone that accepts you and Chara.** ”

Nightmare gave a small smile to Cross, who knew that this was a genuine smile. Nightmare was truly happy for Cross. Cross smiled in return, he glanced at Error then back to Nightmare and did a small grabby motion. Nightmare was like an older brother to Cross, he’d never really had anyone other than Chara and Ink for the longest time. Nightmare gave another smile and pulled Cross over to his throne and gave him a quick hug. “Thank you, Nightmare.” was all Cross said before pulling away and waving to them. He had some reading to do.

**Author's Note:**

> so I tried to post this before then my computer decided to reboot so it's a little rushed. Sorry! the next one will be better! Thanks for reading!


End file.
